1. Field of the Invention
The invention relates to a printing apparatus, and more particularly, to a printing apparatus combining multi-drop and multi-pass printing processes, using quotient distribution and remainder allocation to implement multi-level printing.
2. Description of Prior Art
Please refer to FIG. 1 of a schematic diagram of a constituting structure of a prior art printing apparatus 10. The printing apparatus 10 has a controller 150, a paper-conveying device 140 and an ink jet print head 100 capable of moving along a track 170. The ink jet print head 100 has a plurality of nozzles 110 (only four nozzles 110 are shown in FIG. 1). The printing apparatus 10 is used to print words or images on a document 20. The document 20 has a printing area 30 that is divided into many jetting positions 50. Each square in the printing area 30 of FIG. 1 is a jetting position. During a printing process, the controller 150 controls the ink jet print head 100 to move along track 170 and controls the paper-conveying device 140 to move the document 20 forward (perpendicular to the track 170 in FIG. 1) so that the inkjet print head 100 covers all jetting positions 50 of the printing area 30. In the process of covering the printing area 30 by the ink jet print head 100, each nozzle 110 of the ink jet print head 100 corresponds to a jetting position.
To achieve the effect of multi-level printing, the ink jet print head 100 prints a plurality of ink spots in the same jetting position 50. Printing different amounts of ink spots on the same jetting position can achieve color levels of different concentrations and demonstrate the effect of multi-level printing to show rich levels of printing.
In a prior art printing apparatus using multi-drop printing to implement multi-level printing, an ink jet print head skims the jetting position once and prints a plurality of ink spots on the jetting position. In this prior art, a maximum number of ink spots a printing apparatus can print on the same jetting position determine the number of color levels the printing apparatus can print. If the printing apparatus can print sixteen ink spots on a jetting position, the printing apparatus can print seventeen color levels from 0 to 16.
Another prior art printer of U.S. Pat. No. 5,923,349 uses software to control the ink jet print head to implement multi-level printing by a multi-pass printing process. The ink jet print head of the printer prints only one ink spot on each jetting position, but the ink jet print head skims a jetting position once in each printing pass. Accumulation of ink spots in each printing pass on the same jetting position has an effect of multi-level printing. In this prior art, if the printer can perform four printing passes on the same jetting position, the printer can demonstrate five color levels of 0 to 4. To decide which printing passes to print the predetermined ink spots in a jetting position, the prior art printer uses a series of print masks. The prior art printer uses a print mask to determine which jetting position is to be printed with ink spots in each printing pass. If the prior art printer wants to print seventeen color levels of 0 to 16, the prior art printer prints sixteen times. A lot of time is therefore wasted in doing this. Also each printing pass needs a corresponding print mask and storing these print masks uses a lot of memory. The prior art printer has to determine which jetting position to print ink spots according to the corresponding print mask in each printing pass. Printing speed and efficiency are thus reduced.
It is therefore a primary objective of the present invention to provide a printing apparatus to solve the mentioned problem.
According to the claimed invention, the printing apparatus uses an ink jet print head to perform printing passes on a printing area. The ink jet print head has a plurality of nozzles that are capable of forming an ink spot on an ink jetting position on the printing area during a printing pass according to a predetermined printing method. The predetermined printing method distributes a total number of ink spots on the ink jetting position across a plurality of printing passes according to a quotient and a remainder so that a spot count on the ink jetting position is almost equal for each printing pass.
It is an advantage of the present invention that the printing apparatus according to the present invention combines a multi-drop/multi-pass printing process, and a concept of quotient distribution and remainder allocation to implement multi-level printing to replace print masks so that print time is greatly reduced and only one print mask is needed, therefore reducing memory usage.
These and other objects and the advantages of the present invention will no doubt become obvious to those of ordinary skill in the art after having read the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings.